1. Field of the Invention
The present invention relates to a liquid application apparatus and method, and more particularly to liquid application technology which is suitable as a device for depositing treatment liquid on a recording medium with an object of promoting aggregation of coloring material or the like, prior to ejecting ink droplets in an inkjet recording apparatus, and to an image forming apparatus which uses this technology.
2. Description of the Related Art
In recent years, in order to achieve high quality in an inkjet recording apparatus, it has been proposed that a treatment liquid such as an aqueous solution of a polyvalent metal salt, or an acidic aqueous solution, or the like, be deposited on a recording medium before ejecting droplets of ink, and caused to react with the ink. As a liquid application mechanism for applying this treatment liquid to the recording medium, Japanese Patent Application Publication No. 2007-83180 discloses a liquid application apparatus which comprises: an application roller that rotates in contact with a recording medium, and a liquid holding member which holds an application liquid in a liquid holding space formed between the roller surface and itself by abutting against the circumferential surface (application surface) of the application roller.
The liquid application apparatus described in Japanese Patent Application Publication No. 2007-83180 is based on a mechanism which supplies an application liquid to the circumferential surface of an application roller from a liquid holding space by rotating the application roller, while transferring the application liquid to a recording medium, and in order to prevent the evaporation of the application liquid held in the liquid holding member, a structure is adopted in which abutting members (sliding seal members) having a low sliding friction are provided against the rotating circumferential surface of the application roller in the portions corresponding to the inlet (return side) and the outlet.
However, there is a problem with the structure disclosed in Japanese Patent Application Publication No. 2007-83180 in that the liquid volume which is taken out onto the circumferential surface of the application roller from the liquid holding space of the liquid holding member due to the rotation of the application roller is arbitrary, and the application volume is not stable. Furthermore, when the printing operation is halted (off), there is a possibility that the soluble fractions separate from the liquid adhering to the surface of the application roller which has not been applied.
Moreover, of the application liquid deposited on the surface of the application roller, the application liquid in an untransferred state which is left on the roller rather than being transferred to the recording medium makes contact with the abutting member on the return side of the liquid holding member, and hence there is a possibility that the application liquid collects on the contacting portion on the return side and overflows.